Writing my own Add-On: .deb installs and service running, but won't show in GUI

I've written a very simple add-on based on the samples in the SDK. The .deb file installs successfully onto the device, and the service is running (after invoking `rn_nml -S` in postinst. But it does not show up as an installed app on the GUI. Has anyone seen something like this before?

I've extracted my generated .deb and compared it to others published by the community, and can't spot any differences which would cause this behavior.